Workers exposed to machining fluid aerosols may have an increased risk in developing a variety of respiratory and skin diseases. About 1.2 million workers in the United States are occupationally exposed to metalworking fluids (MWFs). Recent studies have suggested that microorganisms dispersed from MWFs can cause severe respiratory diseases in workers. However, insufficient information is available on the composition and concentration of airborne microorganisms at metalworking sites. Furthermore, the dispersion of mist and microorganisms from MWFs is poorly understood. We plan to study the aerosolization of mist and microorganisms from MWFs using our new techniques for the aerosolization and measurement of bioaerosols. A key instrument in this 2-year study is our newly developed BioSampler designed for long-term sampling of bioaerosols. Experiments will first be performed in the laboratory under controlled conditions by simulating several different machining conditions. A laboratory-scale mist generator, developed by scientists at Milacron Inc., will be adopted and modified for this study, and will be used with MWFs representing different viscosity and surface tension. The aerosolization of mist will be tested first with clean fluids, with fluids inoculated with known concentrations of test microorganisms, and finally with used fluids collected from field test sites. The last phase is a field study. Comparison of the field data with the laboratory data will allow us to interpret the dispersion of mist and microorganisms in MWF environments and to assess the potential microbial exposure of workers. Both are needed developing engineering control strategies. The field study will also help us create an initial database on the concentrations of airborne microorganisms in MWF environments. The findings of this project are expected to contribute toward setting or modifying standards for reducing the health hazards related to MWF exposure.